Many medical procedures require implanting devices and/or introducing instruments through the vascular system or other anatomical passageways. For example, catheters are commonly inserted into the patient through the femoral artery and pass through the vascular system to implant electrodes, stents, and other devices in or near the heart. Other applications include positioning thrombectomy devices, balloon catheters, tissue welding devices, and other types of devices in or near the heart in a similar manner. One aspect of implanting and operating such devices in the patient is to position the distal end of the catheter at a desired target site.
Catheters and other instruments are typically guided to a target site using angiography techniques in which a radiopaque contrast agent or dye is injected into a particular artery or vein as the patient is continuously X-rayed using a fluoroscope. The contrast agent reveals the shape of the vein, and a radiopaque marker on the instrument shows up as a darker point within the vein on fluoroscopic images. Using the fluoroscope, a practitioner can guide the instrument through the vein to locate the instrument at the target site. One problem of angiography techniques, however, is that the patient is continually irradiated. Additionally, the practitioners are also at risk of being irradiated. Therefore, it would be desirable to develop a different technique for tracking instruments through the patient that augments or replaces procedures using fluoroscopes.
One non-ionizing technique for guiding instruments through the throat or vascular system is to use wired magnetic transponders on the instruments. In these applications, the instruments include a coil and a lead wire coupled to the coil. The lead wire extends along the length of the instrument so that it can be connected to a power source or a sensor located externally of the patient. In operation, a field generator sends electrical pulses through the lead wire to generate a pulsed magnetic field from the coil, and external sensors sense the magnetic field produced by the coil. Alternatively, an external source can generate a pulsed magnetic field, and the coil on the instrument acts as a sensor that sends a response signal through the lead wire to a computer. In either case, either the excitation signal or the response signal is transmitted via the lead wire coupled to the coil. One problem with such wired magnetic transponders is that the lead wire occupies space within the catheter. This can limit the capacity and the flexibility of the catheter. Another problem of such wired magnetic transponders is that integrating the lead wire and the coil into the catheter body increases the cost and complexity of producing the catheters. Therefore, wired magnetic tracking systems have not been widely accepted.